Field of the Invention
The present invention relates to a heating fixing apparatus used in an image forming apparatus.
Description of the Related Art
Conventionally, an electrophotographic process is used in an image forming apparatus, such as an electrophotographic copying machine and an electrophotographic printer, and a fixing unit applies a heat fixing process to a toner image formed on a recording medium. A release wax is often included as a constituent material of electrophotographic toner in recent years. The release wax is included to adjust glossiness of a print image or to provide an effect of dispersibility of a pigment, and the release wax is added to prevent a fixation offset.
There are several types of phenomena of fixation offsets as illustrated below. When heating of a fixing member is insufficient (low temperature) in a fixing process on a recording medium, toner is not sufficiently melted, and fixing strength on the recording medium is small. Therefore, part of the toner is attached to the member. This phenomenon is called a cold offset, and the part of the fixing member with the toner appears as a defect of an image on the recording medium. The fixing strength of the fixed toner is weak, and the toner may be peeled off from the recording medium due to friction or the like. On the other hand, although the toner is sufficiently melted when the temperature of the fixing member is too high, viscosity is reduced. Part of the melted toner is peeled off from the recording medium, and the surface of the fixing member is contaminated. This phenomenon is called a hot offset that causes an image defect on the recording medium as in the cold offset.
Adding a wax component as a release agent to the toner is proposed in order to prevent the fixation offsets (Japanese Patent Application Laid-Open No. H08-184992). The release wax is included in the toner, and the release wax moves to an interface between the melted toner and the fixing member during heating and fixing. In this way, offset resistance can be improved. A technique of adding two or more types of release waxes to the toner is also proposed in order to improve the offset resistance (Japanese Patent Application Laid-Open No. 2000-3070).
Although a toner image is fixed on the recording medium by heating the toner in the fixing apparatuses, ultra-fine particles (UFP) may be generated from the toner or grease due to heat during heating.